1. Field of the Invention
In general, the present invention relates to the production of synthetic faujasites or zeolites and more especially to Zeolite Y.
2. Description of the Prior Art
Certain naturally occurring hydrated metal aluminum silicates are called zeolites. The synthetic adsorbents of the invention have compositions similar to some of the natural zeolites. The most common of these zeolites are sodium zeolites.
Zeolites are useful as detergent builders, cracking catalysts and molecular sieves.
Zeolites consist basically of a three-dimensional frame work of SiO.sub.4 and AlO.sub.4 tetrahedra. The tetrahedra are crosslinked by the sharing of oxygen atoms so that the ratio of oxygen atoms to the total of the aluminum and silicon atoms is equal to two or 0/(Al+Si)=2. The electrovalence of each tetrahedra containing aluminum is balanced by the inclusion in the crystal of a cation, for example, a sodium ion. This balance may be expressed by the formula Al/Na=1. The spaces between the tetrahedra are occupied by water molecules prior to dehydration.
Zeolite Y may be distinguished from other zeolites and silicates on the basis of their X-ray powder diffraction patterns and certain physical characteristics. The X-ray patterns for several of these zeolites are described below. The composition and density are among the characteristics which have been found to be important in identifying these zeolites.
The basic formula for all crystalline sodium zeolites may be represented as follows: EQU Na.sub.2 O.Al.sub.2 O.sub.3.xSio.sub.2.yH.sub.2 O.
In general, particular crystalline zeolite will have values for "x" and "y" that fall in a definite range. The value "x" for a particular zeolite will vary somewhat since the aluminum atoms and the silicon atoms occupy essentially equivalent positions in the lattice. Minor variations in the relative number of these atoms do not significantly alter the crystal structure or physical properties of the zeolite. For zeolite Y, an average value for "x" is about 4.5 with the "x" value falling within the range 4.5.+-.0.5.
The value of "y" is not necessarily an invariant for all samples of zeolites. This is true because various exchangeable ions are of different size, and, since there is no major change in the crystal lattice dimensions upon ion exchange, the space available in the pores of the zeolites to accommodate water molecules varies.
The formula for zeolite Y may be written as follows: EQU 0.9.+-.0.2Na.sub.2 O.Al.sub.2 O.sub.3.4.5.+-.1.5SiO.sub.2.yH.sub.2 O;
and, "y" may be any value up to 9.
The pores of zeolites normally contain water.
The above formulas represent the chemical analysis of zeolite Y. When other materials as well as water are in the pores, chemical analysis will show a lower value of "y" and the presence of other adsorbates. The presence in the crystal lattice of materials volatile at temperatures below about 600.degree. C. does not significantly alter the usefulness of the zeolites as an adsorbent since the pores are usually freed of such volatile materials during activation.
Among the ways of identifying zeolites and distinguishing them from other zeolites and other crystalline substances, the X-ray powder diffraction pattern has been found to be a useful tool. In obtaining X-ray powder diffraction patterns, standard techniques are employed. The radiation is the K.alpha. doublet of copper, and a Geiger counter spectrometer with a strip chart pen recorder is used. The peak heights, I, and the positions as a function of 2.theta. where .theta. is the Bragg angle, are read from the spectrometer chart. From these, the relative intensities, 100I/I.sub.0, where I.sub.0 is the intensity of the strongest line or peak, and "d" the interplanar spacing in .ANG. corresponding to the recorded lines are calculated.
X-ray powder diffraction data for sodium zeolite Y are given in Table A. Relative Intensity (100I/I.sub.0) and the "d" values in angstroms (.ANG.) for the observed lines for zeolite Y are shown. In a separate column are listed the sum of the squares of the Miller indices (h.sup.2 +k.sup.2 +l.sup.2) for a cubic unit cell that corresponds to the observed lines in the X-ray diffraction patterns.
Occasionally, additional lines not belonging to the pattern for the zeolite appear in a pattern along with the X-ray lines characteristic of that zeolite. This is an indication that one or more additional crystalline materials are mixed with the zeolite in the sample being tested. Frequently, these additional materials can be indicated as initial reactants in the synthesis of the zeolite, or as other crystalline substances. When the zeolite is heat treated at temperatures of between 100.degree. C. and 600.degree. C. in the presence of water vapor or other gases or vapors, the relative intensities of the lines in the X-ray pattern may be appreciably changed from those existing in the unactivated zeolite pattern. Small changes in line positions may also occur under these conditions. These changes in no way hinder the identification of these X-ray patterns as belonging to the zeolite.
TABLE A ______________________________________ X RAY DIFFRACTION PATTERN FOR SYNTHETIC FAUJASITE (ZEOLITE Y) Relative h.sup.2 + k.sup.2 + l.sup.2 d (.ANG.) Intensity ______________________________________ 3 14.29 100 8 8.75 9 11 7.46 24 19 5.68 44 27 4.76 23 32 4.38 35 40 3.91 12 43 3.775 47 48 3.573 4 51 3.466 9 56 3.308 37 59 3.222 8 67 3.024 16 72 2.917 21 75 2.858 48 80 2.767 20 83 2.717 7 88 2.638 19 91 2.595 11 108 2.381 6 123 2.232 2 128 2.188 4 131 2.162 3 139 2.099 5 144 2.062 3 164 1.933 2 168 1.910 3 179 1.850 2 187 1.810 2 192 1.786 1 195 1.772 2 200 1.750 4 211 1.704 5 ______________________________________
The particular X-ray technique and/or apparatus employed, the humidity, the temperature, the orientation of the powder crystals and other variables, all of which are well known and understood to those skilled in the art of X-ray crystallography or diffraction can cause some variations in the intensities and positions of the lines. These changes, even in those few instances where they become large, pose no problem to the skilled X-ray crystallographer in establishing identities. Thus, the X-ray data given herein to identify the lattice for a zeolite, are not to exclude those materials, which, due to some variable mentioned or otherwise known to those skilled in the art, fail to show all of the lines, or show a few extra ones that are permissible in the cubic system of that zeolite, or show a slight shift in position of the lines, so as to give a slightly larger or smaller lattice parameter.
A simple test described in "American Mineralogist," Vol. 28, Page 545, 1943, permits a quick check of the silicon to aluminum ratio of the zeolite. According to the description of the test, zeolite minerals with a three-dimensional network that contains aluminum and silicon atoms in an atomic ratio of Al/Si=2/3=0.67, or greater, produce a gel when treated with hydrochloric acid. Zeolites having smaller aluminum to silicon ratios disintegrate in the presence of hydrochloric acid and precipitate silica. These tests were developed with natural zeolites and may vary slightly when applied to synthetic types.
U.S. Pat. No. 2,882,244 describes a process for making a synthetic faujasite of the type of zeolite X comprising preparing a sodium-aluminum-silicate water mixture having an SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of from 3:1 to 5:1, an Na.sub.2 O/SiO.sub.2 mole ratio from 1.2:1 to 1.5:1, and an H.sub.2 O/Na.sub.2 O mole ratio of from 35:1 to 60:1, maintaining the mixture at a temperature of from 20.degree. C. to 120.degree. C. until zeolite X is formed, and separating the zeolite X from the mother liquor.
In U.S. Pat. No. 3,119,659, a kaolin clay and sodium hydroxide are formed into a compact body, dried, reacted in an aqueous mixture at a temperature of from 20.degree. C. to 175.degree. C. until a zeolite is formed. A synthetic faujasite of the type of zeolite Y is formed in a reaction mixture having an Na.sub.2 O/SiO.sub.2 molar ratio of 1.5:1, an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of 5:1, and an H.sub.2 O/Na.sub.2 O molar ratio of 30:1 to 60:1. Zeolite Y is formed in a reaction mixture having an Na.sub.2 O/SiO.sub.2 molar ratio of 0.5:1, an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of 20:1 to 40:1.
U.S. Pat. No. 3,920,789 discloses a process for making zeolite Y using elevated temperatures and pressures for the crystallization stage followed by very rapid cooling of the reaction mass.
In U.S. Pat. No. 3,130,007, zeolite Y is formed by preparing an aqueous sodium alumino silicate mixture having a certain composition, maintaining the mixture at a temperature of 20.degree. C. to 125.degree. C. until zeolite Y is formed, and separating the zeolite Y from the mother liquor. Table B shows reaction mixture compositions that produce zeolite Y.
TABLE B ______________________________________ U.S. PAT. NO. 3,130,007 REACTION MIXTURE COMPOSITIONS FOR ZEOLITE Y Na.sub.2 O/SiO.sub.2 SiO.sub.2 /Al.sub.2 O.sub.3 H.sub.2 O/Na.sub.2 O ______________________________________ 0.20-0.40 10-40 25-60 0.41-0.60 10-30 20-60 0.61-1.0 7-30 20-60 0.6-1.0 8-30 12-90 1.5-1.7 10-30 20-90 1.9-2.1 10 40-90 ______________________________________
U.S. Pat. No. 3,130,007 indicates in Column 2, lines 35-42, the necessity of using an active silica source by specifying that aqueous colloidal silica sols or reactive amorphous solid silicas are preferred.
In U.S. Pat. No. 4,016,246, zeolite Y is formed by preparing an aqueous alumino silicate reaction mixture by mixing an alumina component and an Na.sub.2 O component with an active hydrate sodium metasilicate to form a certain reaction mixture, than heating the mixture at a temperature of 20.degree. C. to 120.degree. C. until zeolite Y is formed. Table C shows reaction mixture compositions that produce zeolite Y.
TABLE C ______________________________________ U.S. PAT. NO. 4,016,246 REACTION MIXTURE COMPOSITIONS FOR ZEOLITE Y Na.sub.2 O/SiO.sub.2 SiO.sub.2 /Al.sub.2 O.sub.3 H.sub.2 O/Na.sub.2 O ______________________________________ 0.28-0.30 8-10 20-70 0.30-0.31 8-12 20-70 0.31-0.32 8-14 20-70 0.32-0.34 8-16 12-90 0.34-0.40 7-40 12-120 0.4-1.0 5-50 12-120 0.7-1.0 31-50 12-120 ______________________________________
U.S. Pat. No. 4,016,246 also discusses the significance of using an activated source of sodium silicate. In such patent an active hydrated sodium metasilicate is prepared by carefully hydrating sodium metasilicate under specified conditions.
U.S. Pat. No. 4,166,099 discloses a process for preparing crystalline aluminosilicate zeolites, particularly synthetic faujasites such as zeolite type X and zeolite type Y utilizing especially prepared nucleating centers or seeds. Such seed preparation is lengthy and involved.
U.S. Pat. No. 4,164,551 discloses a process for making zeolite Y also utilizing specifically prepared nucleating centers.
From the prior art, one would assume that zeolite Y cannot be made from reaction mixtures having a relatively low water to silica ratio. A H.sub.2 O/SiO.sub.2 ratio of at least about 40:1 would seem to be required to produce zeolite Y of a sufficiently high crystallinity.
U.S. application Ser. No. 299,878 filed on Sept. 8, 1981, now U.S. Pat. No. 4,400,366, discloses a process for making synthetic faujasites of the Zeolite Y type of an exceptionally high crystallinity. Such process requires a substantial water to silica ratio in the reaction mixture. This application is specifically incorporated herein.
The present invention is a modification of this process for making a high crystalline Zeolite Y. Although an excellent or superior Zeolite Y can be made by this exemplary process, substantial amounts of water are required. Present commercial specifications for zeolite Y for most uses do not require such high crystallinity zeolites.
It is therefore an important object of the present invention to provide a synthetic faujasite of the zeolite Y type which meets current specifications for crystallinity for commercial application and which process utilizes a reduced amount of water.
It is another object of the present invention to provide a process for producing a commercially acceptable zeolite Y which is more economical than present processes.
Still another object is to provide a zeolite Y product which has high crystallinity and yet which can be manufactured at reduced costs.
Other objects and advantages of the invention will be more readily apparent from a reading of the description hereinafter.